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تسجيل مستخدم جديدTheory of charged impurity scattering in two dimensional graphene
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We review the physics of charged impurities in the vicinity of graphene. The long-range nature of Coulomb impurities affects both the nature of the ground state density profile as well as graphenes transport properties. We discuss the screening of a single Coulomb impurity and the ensemble averaged density profile of graphene in the presence of many randomly distributed impurities. Finally, we discuss graphenes transport properties due to scattering off charged impurities both at low and high carrier density.
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We have examined the impact of charged impurity scattering on charge carrier transport in bilayer graphene (BLG) by deposition of potassium in ultra-high vacuum at low temperature. Charged impurity scattering gives a conductivity which is supra-linea
r in carrier density, with a magnitude similar to single-layer graphene for the measured range of carrier densities of 2-4 x 10^12 cm^-2. Upon addition of charged impurities of concentration n_imp, the minimum conductivity Sigma_min decreases proportional to n_imp^-1/2, while the electron and hole puddle carrier density increases proportional to n_imp^1/2. These results for the intentional deposition of potassium on BLG are in good agreement with theoretical predictions for charged impurity scattering. However, our results also suggest that charged impurity scattering alone cannot explain the observed transport properties of pristine BLG on SiO2 before potassium doping.
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minimum value sigma_min near twice the conductance quantum 4e2/h[14, 15, 19, 20]. Here we vary the density of charged impurities nimp on clean graphene21 by deposition of potassium in ultra high vacuum. At non-zero carrier density, charged impurity scattering produces the ubiquitously observed1, 14-18 linear sigma_(n) with the theoretically-predicted magnitude. The predicted asymmetry11 for attractive vs. repulsive scattering of Dirac fermions is observed. Sigma_min occurs not at the carrier density which neutralizes nimp, but rather the carrier density at which the average impurity potential is zero10. Sigma_min decreases initially with nimp, reaching a minimum near 4e2/h at non-zero nimp, indicating that Sigma_min in present experimental samples does not probe Dirac-point physics14, 15, 19, 20 but rather carrier density inhomogeneity due to the impurity potential3, 9, 10.
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